In the direct chip attachment (DCA) packaging systems, chips must be replaced if defective chips are found after bonding semiconductor chips on a circuit substrate, or in the case of an engineering change (EC). When chips are face-down bonded using solder bumps and are not resin-encapsulated, the chips may be removed with ease from the substrate by heating the chips to melt the solder bumps.
As shown in FIG. 1, however, when the space between the substrate 2 and the bottom surface of the chip 4 is filled with a resin such as epoxy resin to encapsulate the chip, problems arise. That is, the resin adheres to the chip 4 and the substrate 2, and thus the chip and the resin cannot be removed with ease. If one attempts to forcedly remove the chip and the resin, the substrate or the circuit on the substrate may be damaged and cannot be reused.
Japanese Published Unexamined Patent Application (Patent Kokai) 58-48932 discloses a technique to facilitate the replacement of resin-encapsulated chips in which the surface of a substrate such as glass is coated with a layer of a material such as a silicone resin which does not adhere well to the encapsulation resin in order to prevent the adhesion of the encapsulation resin to the substrate. Chip bumps are connected to electrode pads on the substrate through openings in the resin layer. However, due to weak adhesion between the encapsulation resin and the substrate, this method involves some problems such as insufficient encapsulation and poor mechanical strength of the bond between the chips and the substrate.
Alternatively, a method can be considered in which an encapsulation resin is treated with chemicals such as a solvent to dissolve or decompose it. However, this method has various problems. First, the substrate and components may be affected adversely by the chemicals. Also, in order to subject only a selected chip to the chemical treatment, the chips must be mounted spaced apart from each other by a required distance, and thus the chip density is limited. Furthermore, since the distance between the chip and the substrate is as small as, for example, 0.1 mm, it is difficult to remove the resin by introducing the chemicals into this space, increasing treatment time.
Furthermore, when a chip bonded face down by bump electrodes such as solder bumps is removed, the bump electrodes are destroyed. In replacing a chip, therefore, proper bump connections must be reconstructed. Also, when a resin encapsulated chip is removed, the resin encapsulation is also damaged and thus it must be done again. These operations must be easily performed, and the reliability of the replacement chip must be maintained.